Digital currency systems such as the Bitcoin digital currency system involve a process of “mining” or coin production that consumes vast computational resources. Bitcoin is a monetary system based on the equivalence “time=money.” Time in this sense refers to computation time, while money in this sense refers to units of payment also referred to as Bitcoins. Bitcoins are generated and used in a peer-to-peer computing network. To generate a batch of coins in the Bitcoin system, clients perform an operation called mining. Mining coins requires solving a computationally intensive problem which involves repeated cryptographic hashing. Thus, a coin represents an investment of computational resources.